Embedded magnetic component transformer device

ABSTRACT

An embedded transformer device includes first, second, and auxiliary windings, defined in an insulating substrate by conductive vias joined together by conductive traces. The positions of the conductive vias are arranged to optimize the isolation properties of the transformer and to reduce the coupling of the transformer by increasing the leakage inductance. The embedded transformer device provides better isolation between input side and output side windings, and allows an oscillating LC circuit to be set up in the case of a short circuit, preventing high power from extending between the input and output terminals and thereby avoiding damage to the connected electrical components.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an embedded magnetic componenttransformer device, and in particular to an embedded magnetic componenttransformer devices with reduced coupling and improved isolationproperties.

2. Description of the Related Art

It is known, for example, in US 2011/0108317 A1, to provide low profiletransformers and inductors in which the magnetic components are embeddedin a cavity in a resin substrate, and the necessary input and outputelectrical connections for the transformer or inductor are formed on thesubstrate surface. A printed circuit board (PCB) for a power supplydevice can then be formed by adding layers of solder resist and copperplating to the top and/or bottom surfaces of the substrate. Thenecessary electronic components for the device may then be surfacemounted on the PCB.

Compared to conventional transformers, an embedded design allows asignificantly thinner and more compact device to be built. This isdesirable because typically the space available for mounting thetransformer device onto a PCB, for example, a motherboard of anelectronics device, will be very limited. A transformer component with asmaller footprint will therefore enable more components to be mountedonto the PCB, or enable the overall size of the PCB and therefore theentire device to be reduced.

When reducing the size of the transformer device, the gap betweenadjacent turns on a transformer winding are likely to be provided moreclosely together, and the gap between separate windings provided on thetransformer will also be reduced. This reduces the ease with which amagnetic field, set up in the transformer during use, can escape fromthe transformer core and therefore results in a stronger coupling, viathe magnetic field, between the separate windings provided on the core.Another consequence of reducing the gap between adjacent turns is anincrease in the capacitance existing between adjacent conductingcomponents which include the transformer windings. Such increasedcoupling between the windings via the magnetic field they generate, andsuch increased distributed capacitance throughout the transformer, arenot desirable properties for a transformer in certain applications.

Furthermore, reducing the transformer size can result in safetyconsiderations, particularly if two separate windings sharing a commontransformer core are to handle high voltages. Such a transformer is usedin power electronics applications and power converter technology, forexample. In this case, the windings must be electrically isolated fromone another. A smaller transformer will tend to reduce the distancebetween electrically isolated windings, meaning that the electricalisolation is less robust against failure by electrical arcing andreducing the maximum voltages that the transformer windings can safelyhandle.

The electrical isolation can be increased to a safe level by using amulti-layer PCB arrangement with different windings provided ondifferent PCB layers, by providing a cover on the transformer core, orby coating the windings in a conformal coating or other sort ofinsulating material such as insulating tape. Triple insulated wire canalso be used. However, all of these techniques have the disadvantagethat the embedded magnetic component transformer device must be madelarger to accommodate the extra PCB layers or the thicker insulation onthe windings and/or core.

It would be desirable to provide an embedded transformer device havingreduced coupling between the coils and improved isolationcharacteristics, and to provide a method for manufacturing such adevice.

SUMMARY OF THE INVENTION

A preferred embodiment of the present invention provides an embeddedtransformer device including: an insulating substrate including a firstside and a second side opposite the first side, and including a cavitytherein, the cavity including an inner and an outer periphery; amagnetic core housed in the cavity including a first section and asecond section; a first winding, extending through the insulatingsubstrate and around the first section of the magnetic core; a secondwinding, extending through the insulating substrate and around thesecond section of the magnetic core. Each of the first and secondwindings include: upper conductive traces located on the first side ofthe insulating substrate; lower conductive traces located on the secondside of the insulating substrate; inner conductive connectors extendingthrough the insulating substrate adjacent to the inner periphery of themagnetic core, the inner conductive connectors respectively definingelectrical connections between respective upper conductive traces andrespective lower conductive traces; and outer conductive connectorsextending through the insulating substrate adjacent to the outerperiphery of the magnetic core, the outer conductive connectorsrespectively defining electrical connections between respective upperconductive traces and respective lower conductive traces. The innerconductive connectors of the first winding are arranged in a pluralityof curved rows, each curved row being positioned at a constant orsubstantially constant distance from the inner periphery of the cavity.The inner conductive connectors of the second winding are arranged in afirst curved row positioned at a constant or substantially constantdistance from the inner periphery of the cavity, and the constant orsubstantially constant distance being large enough to allow a secondcurved row of inner conductive connectors to be accommodated between thefirst curved row and the inner periphery of the cavity. The outerconductive connectors of the second winding are arranged in a firstcurved row positioned at a constant or substantially constant distancefrom the outer periphery of the cavity, and the constant orsubstantially constant distance being large enough to allow a secondcurved row of outer conductive connectors to be accommodated between thefirst curved row and the outer periphery of the cavity.

The inner conductive connectors of the first winding on the curved rowclosest to the inner periphery of the cavity may be arranged on a firstcircular or substantially circular arc having a first radius; the innerconductive connectors of the second winding on the first curved row maybe arranged on a second circular or substantially circular arc,concentric to the first circular or substantially circular arc, having asecond radius; and the first radius may be greater than the secondradius.

The first winding may be spaced apart from the second winding so thatelectrical isolation is provided between the first winding and thesecond winding.

The embedded transformer device may further include: a first isolationbarrier located on the first side of the insulating substrate, coveringat least a portion of the first side between the first winding and thesecond winding where the first winding and second winding are closest,and defining a solid bonded joint with the first side of the insulatingsubstrate; and a second isolation barrier located on the second side ofthe insulating substrate covering at least a portion of the second sidebetween the first winding and the second winding where the first windingand second winding are closest, and defining a solid bonded joint withthe second side of the insulating substrate.

The embedded transformer device may further include: an auxiliarywinding, extending through the insulating substrate and around themagnetic core, the auxiliary winding including: upper conductive traceslocated on the first side of the insulating substrate; lower conductivetraces located on the second side of the insulating substrate; innerconductive connectors extending through the insulating substrateadjacent to the inner periphery of the magnetic core, the innerconductive connectors respectively forming electrical connectionsbetween respective upper conductive traces and respective lowerconductive traces; and outer conductive connectors extending through theinsulating substrate adjacent to the outer periphery of the magneticcore, the inner conductive connectors respectively defining electricalconnections between respective upper conductive traces and respectivelower conductive traces; wherein the inner conductive connectors of theauxiliary winding are arranged in a plurality of curved rows, eachcurved row being positioned at a constant or substantially constantdistance from the inner periphery of the cavity.

The auxiliary winding may be spaced apart from the second winding sothat electrical isolation is provided between the auxiliary winding andthe second winding.

The electrical isolation may be provided by the minimum of: the minimumdistance of separation between the first winding and the second winding;and the minimum distance of separation between the second winding andthe magnetic core.

The constant or substantially constant distance being large enough toallow a second curved row of outer conductive connectors to beaccommodated may increase the leakage inductance of the transformer.

A leakage inductance of the transformer and a distributed capacitance ofthe transformer windings may define a high-frequency oscillating LCcircuit, operable to limit the power transfer between the first andsecond windings when a short circuit occurs.

A power converter including the embedded transformer device may beprovided.

The power converter may further include circuitry to energize thetransformer windings, wherein the circuitry is a Royer circuit.

A preferred embodiment of the present invention provides an embeddedtransformer device including: an insulating substrate including a firstside and a second side opposite the first side, and including a cavitytherein, the cavity including an inner and an outer periphery; amagnetic core housed in the cavity including a first section and asecond section; a first winding, extending through the insulatingsubstrate and around the first section of the magnetic core; a secondwinding, extending through the insulating substrate and around thesecond section of the magnetic core; each of the first and secondwindings including: upper conductive traces located on the first side ofthe insulating substrate; lower conductive traces located on the secondside of the insulating substrate; inner conductive connectors extendingthrough the insulating substrate adjacent to the inner periphery of themagnetic core, the inner conductive connectors respectively definingelectrical connections between respective upper conductive traces andrespective lower conductive traces; and outer conductive connectorsextending through the insulating substrate adjacent to the outerperiphery of the magnetic core, the outer conductive connectorsrespectively defining electrical connections between respective upperconductive traces and respective lower conductive traces. The innerconductive connectors of the first winding are arranged in one or morecurved rows, each curved row being positioned at a constant orsubstantially constant distance from the inner periphery of the cavity.The inner conductive connectors of the second winding are arranged inone or more curved rows, each curved row being positioned at a constantor substantially constant distance from the inner periphery of thecavity. The minimum distance between the inner conductive connectors ofthe second winding and the magnetic core is greater than the minimumdistance between the inner conductive connectors of the first windingand the magnetic core.

Preferred embodiments of the present invention also includecorresponding methods of manufacture.

The above and other features, elements, characteristics, steps, andadvantages of the present invention will become more apparent from thefollowing detailed description of preferred embodiments of the presentinvention with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1G illustrate an example technique for manufacturing anembedded magnetic component device.

FIG. 2 illustrates a first preferred embodiment of the present inventionin a top down view of the conductive vias forming a windingconstruction.

FIG. 3 illustrates the arrangement of the conductive vias in FIG. 2 andthe inter-via and winding distances.

FIG. 4 illustrates the trace pattern for the arrangement of conductivevias in FIGS. 2 and 3.

FIG. 5 illustrates a preferred embodiment of the present invention wherethe embedded transformer device defines a portion of a self-oscillatingpush-pull circuit.

FIG. 6 is a graph showing high-frequency oscillations of the transformervoltage during a short circuit mode.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Preferred embodiments of the present invention include an embeddedmagnetic component transformer device including first, second, andauxiliary windings extending around a magnetic core embedded in asubstrate. The embedded magnetic component transformer device mayadvantageously be used as a portion of switching power electronicdevices, such as a Royer circuit. A first preferred embodiment of thepresent invention is illustrated in FIGS. 2 to 6 which will be discussedin detail below.

For ease of understanding, an example method of manufacturing anembedded magnetic component transformer device will now be describedwith reference to FIGS. 1A to 1F. Techniques for manufacturing anembedded magnetic component transformer device are described in UKpatent applications GB 1414469.5 and GB 1414468.7 filed by the presentapplicant, the entire contents of which are incorporated herein byreference.

In a first step of the method, illustrated in FIG. 1A, a circularannulus or cavity 302 for housing a magnetic core is routed in aninsulating substrate 301. In this example, the insulating substrate isformed of a resin material, such as FR4. FR4 is a composite ‘pre-preg’material composed of woven fiberglass cloth impregnated with an epoxyresin binder. The resin is pre-dried, but not hardened, so that when itis heated, it flows and acts as an adhesive for the fiberglass material.FR4 has been found to have favorable thermal and insulation properties.

As shown in FIG. 1B, a circular magnetic core 304 is then installed inthe cavity 302. The cavity 302 may be slightly larger than the magneticcore 304, so that an air gap may exist around the magnetic core 304. Themagnetic core 304 may be installed in the cavity manually or by asurface mounting device such as a pick and place machine.

In the next step, illustrated in FIG. 1C, a first insulating layer orcover layer 305 is secured or laminated on the insulating substrate 301to cover the cavity 302 and the magnetic core 304. Preferably, the coverlayer 305 is formed of the same material as the insulating substrate 301as this aids bonding between the top surface of the insulating substrate301 and the lower surface of the cover layer 305. The cover layer 305may therefore also be formed of a material such as FR4, laminated ontothe insulating substrate 301. Lamination may be via adhesive or via heatactivated bonding between layers of pre-preg material. In otherpreferred embodiments of the present invention, other materials may beused for the layer 305.

In the next step illustrated in FIG. 1D, though-holes 306 are formedthrough the insulating substrate 301 and the cover layer 305. Thethrough holes 306 are formed at suitable locations to define the firstand second coil conductor windings of an embedded transformer. The exactarrangement of the through-holes 306 will be described later, but ageneral pattern of through-holes including two arcs corresponding to theinner and outer circular circumferences of the cavity 302 is shown inFIG. 1D. As is known in the art, the through-holes 306 may be formed bydrilling, or any other suitable technique.

As shown in FIG. 1E, the though-holes 306 are then plated to formconductive via holes 307 that extend from the top surface of the coverlayer 305 to the bottom surface of the substrate 301. Conductive ormetallic traces 308 are added to the top surface of the cover layer 305to define an upper winding layer connecting the respective conductivevia holes 307, and to form a portion of the windings of the transformer.The upper winding layer is illustrated by way of example in the righthand side of FIG. 1E. The metallic traces 308 and the plating for theconductive via holes 307 are usually formed from copper, and may beformed in any suitable way, such as by adding a copper conductor layerto the outer surfaces of the layer 305 which is then etched to form thenecessary patterns, deposition of the copper onto the surface, and soon.

Metallic traces 308 are also formed on the bottom surface of theinsulating substrate 301 to define a lower winding layer also connectingthe respective conductive via holes 307 to a portion the windings of thetransformer. The upper and lower winding layers 308 and the via holes307 together define the windings of the transformer. In thisillustration, only first and second side windings are illustrated.

As shown in FIGS. 1F and 1G, optional second and third insulating layers309 may be formed on the top and bottom surfaces of the structure shownin FIG. 1E to define first and second isolation barriers. The layers maybe secured in place by lamination or any other suitable technique.

In FIG. 1F, the bottom surface of the second insulating layer or firstisolation barrier 309 a adheres to the top surface of the cover layer305 and covers the terminal lines 308 of the upper winding layer. Thetop surface of the third insulating layer or second isolation barrier309 b on the other hand adheres to the bottom surface of the substrate301 and so covers the terminal lines 308 of the lower winding layer.Advantageously, the second and third insulating layers, i.e., firstisolation barrier 309 a and second isolation barrier 309 b, may also beformed of FR4, and so laminated onto the insulating substrate 301 andcover layer 305 using the same process as for the cover layer 305.

Through-holes and via conductors are formed through the second and thirdinsulating layers, i.e., first isolation barrier 309 a and secondisolation barrier 309 b, in order to connect to the input and outputterminals of the first and second transformer windings (not shown).Where the conductive via holes 327 through the second and thirdinsulating layers, i.e., first isolation barrier 309 a and secondisolation barrier 309 b, are located apart from the conductive via holes307 through the substrate 301 and the cover layer 305, a metallic traceis preferably provided on the upper winding layer connecting the inputand output vias to the first and last via in each of the first andsecond windings. Where the input and output vias are formed inoverlapping positions, then conductive or metallic caps could be addedto the first and last via in each of the first and second windings.

In FIG. 1F, the first and second isolation barriers 309 a and 309 bdefine a solid bonded joint with the adjacent layers, either cover layer305 or substrate 301, on which the upper or lower winding layers 308 ofthe transformer are formed. The first and second isolation barriers 309a and 309 b therefore provide a solid insulated boundary along thesurfaces of the embedded magnetic component device, greatly reducing thechance of arcing or breakdown, and allowing the isolation spacingbetween the first and second side windings to be greatly reduced.

The first and second isolation barriers 309 a and 309 b are formed onthe substrate 301 and cover layer 305 without any air gap between thelayers. If there is an air gap in the device, such as above or below thewinding layers, then there would be a risk of arcing and failure of thedevice. The first and second isolation barriers 309 a and 309 b, thecover layer 305 and the substrate 301, therefore define a solid block ofinsulating material.

In FIG. 1F, the first and second isolation barriers 309 a and 309 b areillustrated as covering the whole of the cover layer 305 and the bottomsurface of the substrate 301 of the embedded magnetic component device300. In the alternative preferred embodiment of FIG. 1G, however, it issufficient if the first and second isolation barriers 309 a and 309 bare applied to the cover layer 305 and the bottom of the substrate 301so that they at least cover only the portion of the surface of the coverlayer 305 and substrate 301 surface between the first and secondwindings, where the first and second windings are closest. As shown, thefirst and second isolation barriers 309 a and 309 b may then be providedas a long strip of insulating material placed on the surface parallel orsubstantially parallel to the shorter edge of the device and covering atleast the isolation region between the first and second side windings.In alternative preferred embodiments, as the first and second sidewindings follow the arc of the magnetic core 304 around which they arewound, it may be sufficient to place the isolation barriers 309 a and309 b only where the first and second side windings are closest, whichin this case is at the 12 o'clock and 6 o'clock positions. As notedabove, however, a full layer of the first and second isolation barriers309 a and 309 b covering the entire surface of the embedded componentdevice can be advantageous as it provides locations for further mountingof components on the surface of the device.

A first preferred embodiment of an embedded magnetic componenttransformer device will now be described with reference to FIG. 2. Suchan embedded transformer device may be constructed according to the stepsdescribed in relation to FIGS. 1A to 1F.

As shown in FIG. 2, the embedded magnetic component transformer deviceincludes a first winding in region 310 of the substrate, a secondwinding in the region 320 of the substrate, and an auxiliary winding inthe region 330 of the substrate. These windings are located around acommon magnetic transformer core 304 with an outer periphery 304 a andan inner periphery 304 b provided in the cavity 302. For the purposes ofillustration the regions labelled 310, 320, 330 are respectively boundedby outlines 310 a, 320 a, 330 a. As shown in FIG. 2, the regions 310,320 and 330 are separate from one another and occupy discrete areas ofthe substrate. The windings do not therefore overlap with one another.The central island formed by the cavity 302 may be called the isolationregion as it is designed to provide some isolation between the first andsecond sides of the transformer.

The first, second, and auxiliary windings of the transformer are definedby upper and lower conductive traces formed on the top and bottom of theresin substrate (not visible in FIG. 2), connected by a plurality ofrespective conductive connectors extending through the substrate fromone side to the other. The conductive connectors may be defined byplated via holes as described above, or maybe conductive pins orfilaments. In FIGS. 2, 3, and 4 the conductive connectors areillustrated as plated vias.

The arrangement of the via holes defining the first, second, andauxiliary windings is important because the spacing between the viaholes themselves, together with the spacing between the via holes andthe magnetic core, affects both the electrical isolation obtainablebetween the transformer windings, and the degree of coupling between thetransformer windings.

In practice, the size of the embedded magnetic component transformerdevice limits the extent of the spacing available between the via holes.Nevertheless, it is often desirable to maximize the spacing between thevias because this leads to better isolation performance. Large spacingsalso tend to increase the leakage inductance of the transformer, therebyweakly coupling the windings together. This is often desirable forreasons explained in below. The via hole spacing therefore providesimprovements in the isolation characteristics and leakage inductance ofthe windings, while still allowing a compact transformer device to berealized.

The structure of the separate windings will now be described in moredetail.

The first winding of the transformer, located within region 310,includes first outer conductive vias 311, first inner conductive vias312 a and 312 b, and upper and lower conductive traces linking theconductive vias (not shown in FIG. 2). The first outer conductive vias311 are arranged in one row along the circular portion of the outer edge302 b of the cavity 302, and are split into two groups. The first innerconductive vias on the other hand are arranged in two rows: an outer row312 a which is closest to the inner edge 302 a of the cavity 302, and aninner row 312 b which is adjacent to the outer row 312 a but fartherfrom the inner edge 302 a of the cavity and closer to the center of theisolation region 335.

The first transformer winding may have the same number of inner andouter conductive vias defining the complete first winding. This ensuresthat the terminals at either end of the first winding are on the sameside, for example on top of the cover layer 305 or on the bottom of theinsulating layer. Alternatively, it is also possible to form the firstwinding with an arrangement where there is one more inner conductive viathan there are outer conductive vias, or where there is one fewer innerconductive vias than there are outer conductive vias. Such anarrangement means that the terminals at either end of the first windingare on opposing sides, with one on top of the cover 305 and one on thebottom of the insulating layer. Both of these alternatives, where theterminals are on the same or opposing sides, may be desirable dependingon the location of the input and output circuitry to which the terminalsare to be connected. The second and auxiliary windings may also besimilarly arranged.

As shown in FIG. 2, the outer row 312 a of the first inner conductivevias contains seven conductive vias spaced apart, whereas the inner row312 b of the first inner conductive vias contains nine conductive vias,also spaced apart but with less inter-via spacing than for the outer row312 a. Other configurations are possible, although this will alter theleakage inductance of the embedded transformer as described below. Thefirst outer conductive vias 311 are only arranged in one row, with sixconductive vias in a first group, and with ten conductive vias in asecond group. Other configurations, with a different distribution of theconductive vias between the groups, are also possible. As there aresixteen first inner conductive vias and sixteen first outer conductivevias, the first winding includes sixteen complete turns when theconductive vias are connected by the conducting traces.

The second winding of the transformer includes second outer conductivevias 321, second inner conductive vias 322, and conductive traceslinking the conductive vias (not shown in FIG. 2). The second outerconductive vias 321 are arranged in a single row along the circularportion of the outer edge 302 b of the cavity 302, and as with theconductive vias of the first winding they are split into two groups. Thesecond inner conductive vias are also arranged in a single row 322.

The curved row of second inner conductive vias 322 is provided such thatthe conductive vias are at a constant or substantially constant distancefrom the inner edge 302 a of the cavity 302. The distance between therow of second inner conductive vias 322 and the inner edge 302 a of thecavity 302 is larger than that between the outer row of first innerconductive vias 312 a and the inner edge 302 a of the cavity 302.Preferably, the distance between the row of second inner conductive vias322 and the inner edge 302 a of the cavity 302 is large enough toaccommodate another row of conductive vias between the row 322 and theinner edge 302 a of the cavity 302.

The curved rows of second outer conductive vias 321 are also providedsuch that the conductive vias are at a constant or substantiallyconstant distance from the outer edge 302 b of the cavity 302. Thedistance between the rows of second outer conductive vias 321 and theouter edge 302 b of the cavity 302 is larger than that between the rowof first outer conductive vias 311 and the outer edge 302 b of thecavity 302. Preferably, the distance between the rows of second outerconductive vias 321 and the outer edge 302 b of the cavity 302 is largeenough to accommodate another row of conductive vias between the rows321 and the outer edge 302 b of the cavity.

In the preferred embodiment shown in FIG. 2, the second inner conductivevias 322 include nine conductive vias, and the second outer conductivevias 321 include nine conductive vias, split into one group of fourconductive vias and one group of five conductive vias. Therefore thesecond winding includes nine turns when the conductive vias areconnected by the conducting traces. Other configurations are equallypossible.

The auxiliary winding of the transformer includes auxiliary outerconductive vias 331, auxiliary inner conductive vias 332 a and 332 b,and conductive traces linking the conductive vias (not shown in FIG. 2).The auxiliary outer conductive vias are arranged in one row along thecircular portion of the outer edge 302 b of the cavity 302. Theauxiliary inner conductive vias are arranged in two rows: an outer row332 a which is closest to the inner edge 302 a of the cavity 302, and anouter row 332 b which is adjacent to the outer row 332 a but fartherfrom the inner edge 302 a of the cavity 302.

As shown in FIG. 2, each of the outer row 332 a and inner row 332 b ofthe auxiliary inner conductive vias contains two vias, although otherconfigurations are possible. The auxiliary outer conductive vias 331 areonly provided in one row including five conductive vias. As there arefour auxiliary inner conductive vias, the auxiliary winding includesfive turns when the conductive vias are connected by the conductingtraces.

In some preferred embodiments of the present invention, the voltageacross the auxiliary winding is fed back to the input circuitry beingused to energize the first winding, the auxiliary winding acting as afeedback winding. Alternatively or additionally, the auxiliary windingcan be used to control some other aspect of the input and/or outputcircuitry. Other uses of the auxiliary winding could be to provide ahousekeeping supply or to control a synchronous rectifier. More than oneauxiliary winding could be provided, allowing more than one of thesefunctions to be carried out. Other uses for the auxiliary windings arealso possible.

When the transformer is in operation, the ratio of the voltages providedacross the first, second, and auxiliary windings is proportional to thenumber of turns in each respective winding. Therefore, the number ofturns in each winding can be chosen, by adding or removing conductivevias and conductive traces, in order to obtain desirable voltage ratiosbetween the windings. This is particularly important in, for example,isolated DC to DC converters where strict requirements as to the outputvoltage will typically need to be met.

Optional terminations 340 provided in the substrate of the embeddedtransformer device are also shown. These may take the form of edgecastellations providing for Surface Mount Application (SMA) connectionsfrom the embedded transformer device to a printed circuit board on whichthe embedded transformer device may be mounted. The cover layer 305 isarranged so as not to cover these terminations, to allow them to beconnected to the other electrical components.

As explained above, the spacing between adjacent conductive vias and thespacing between the via holes and the magnetic core has implications forthe electrical isolation between the transformer windings and the amountof leakage inductance present in the transformer device. At the sametime, it is desirable to provide a transformer device with a smallfootprint, thereby limiting the extent to which these spacings can beincreased.

FIG. 3 shows the spacings between the windings and vias in more detail.FIG. 3 shows the identical arrangement of conductive vias shown in FIG.2. Some components have not however been labelled in FIG. 3 for the sakeof clarity. It should nevertheless be understood that all of thecomponents that were labelled and described in relation to FIG. 2 alsoapply to the subsequent figures. For simplicity, the first and auxiliarywindings will be jointly referred to as input side windings, whichoccupy a region 410 bounded by the line 410 a. The second windings willby referred to as output side windings, which occupy a region 420bounded by the line 420 a.

Three different spacings have been taken into consideration in thedesign shown in FIGS. 2 and 3. Distance X1 illustrated in FIG. 3 is theisolation distance or minimum distance between the input side windingsand the output side windings. As can be seen in FIG. 3, the gap in theisolation region 335 separating the input side inner conductive viasfrom the output side inner conductive vias is the minimum gap betweenthe input side and output side windings. It is smaller than the gapoutside the cavity 302 separating the input side outer conductive viasfrom the output side outer conductive vias. Further, the upper and lowerconductive traces of the input side windings and the conductive trace ofthe output side windings that are closest to one another diverge fromeach other as they extend outwards from the center of the cavity 302 tothe outer side of the substrate in a direction from the center of theembedded transformer to its outer edge. This means that distance X1 inthe isolation region 335 is the closest distance between conductive viasof the input side windings and conductive vias of the output sidewindings.

The distance X2 is the minimum distance between the outer 321 and inner322 conductive vias that define the output side (second) windings andthe magnetic core 304. The distance between the upper and lowerconductive traces and the magnetic core 304 is not considered here asthe upper and lower conductive traces are provided above the cover layer305, or below a layer of the insulating substrate provided below thecavity 302, with the result that the traces are better isolated from themagnetic core 304 than the conductive vias 321 and 322. In thearrangement of FIG. 3, this minimum distance occurs at the two locationslabelled X2. As can be understood from FIG. 3, the distance X2 issignificantly greater than the corresponding distance between the innerand outer conductive vias 311, 312, 331, and 332 on the input sidewindings and the magnetic core 304.

Finally, the distance X3 is the distance between the second outerconductive vias 321 and the second inner conductive vias 322. Thisdistance is constant or substantially constant for all of the opposingsecond conductive vias (that is, all pairs of second inner and secondouter conductive vias) that will be joined by a upper and lowerconductive trace. In practice, small variations or tolerances in thedistance are possible.

The significance of the distances X1, X2, and X3 will now be describedwith regard to insuring that the input side windings and output sidewindings are sufficiently isolated electrically from one another.Electrical isolation is necessary to prevent a breakdown in the gapbetween the windings occurring and the transformer windings from beingsubsequently shorted. The level of isolation between the input side andoutput side windings, that is the maximum voltage difference that thetransformer can withstand between the input side and output sidewindings without electrical arcing, is determined by both the directpath between the input side and output side windings themselves and,because the magnetic core 304 is an electrical conductor, by an indirectpath between the windings extending through the magnetic core 304.

The direct path between the input side and output side windings can bemaximized by making the distance X1 as large as possible. The isolationis determined by the minimum distance X1 at the two locations shown inFIG. 3. This may be between the first winding and the second winding, orthe auxiliary winding and the second winding. However, there is apractical limitation on the extent to which this distance can beincreased because of the size of that portion of the insulatingsubstrate enclosed within the magnetic core 304, the isolation region335, which defines a limited space in which all of the inner conductivevias must be necessarily formed. It is undesirable for the centralisolation region 335 and the transformer to be too large because spaceon the circuit board, to which the transformer will be connected, is ata premium. Therefore, as shown in FIGS. 2 and 3, a way of increasing thedistance X1 while still keeping the same number of inner conductive viasis to provide those inner conductive vias on the input side windings inmore than one row, for example, two rows 312 a, 312 b for the firstwinding, and two rows 332 a, 332 b for the auxiliary winding. Thisallows a larger separation between input side and output side innerconductive vias than would be achievable if a single row were used, asvias that would otherwise appear in the gap between the input side andoutput side windings can be accommodated in the second row of vias.Using multiple rows therefore enables the overall size of thetransformer to be reduced compared to using only a single row, whilestill maintaining the required isolation characteristics.

The indirect path between the input side and output side windings, thatis on a path extending through the magnetic core 304, can be maximizedby making the distance between the conductive vias of the input sidewindings and the core 304, or between the conductive vias of the outputside windings and the core 304, as large as possible. As the degree ofisolation will be set by the greater of these two distances, it isnecessary only to consider one of them when setting the size of theindirect isolation path.

In the preferred embodiment of FIGS. 2 and 3, the two-row staggeredarrangement of inner conductive vias provided on the input side requiresthat some of the conductive vias are positioned closely to the magneticcore 304. This is necessary because there are more conductive vias onthe input side than the output side, and is also necessary to maintainthe distance X1 as described above. In contrast, the inner conductivevias on the output side are provided in only a single row, which enablesthem to be positioned further from the magnetic core increasing thedistance X2. The outer conductive vias on the output side are alsoprovided in a single row, again enabling them to be positioned furtherfrom the magnetic core. As shown in FIG. 3, the single row of innerconductive vias on the output side is separated or set back from theinner periphery of the cavity 302 by a distance sufficient toaccommodate another row of vias. In other words, the row of vias closestto the cavity 302 on the input side is not continued around the innerperiphery of the cavity 302 on the output side but is instead omitted toprovide a further isolation gap.

In some preferred embodiments of the present invention, the innerconductive connectors of the first winding 312 a on the curved rowclosest to the inner periphery 302 a of the cavity 302 are arranged on afirst circular or substantially circular arc having a first radius, andthe inner conductive connectors of the second winding 322 are arrangedon a second circular or substantially circular arc. The first and secondcircular arcs are concentric or substantially concentric, that is theyshare the same center. The radius of the first circular arc is greaterthan that of the second circular arc.

In some preferred embodiments of the present invention, the distancebetween the inner periphery 302 a of the cavity 302 and the second innerconductive vias 322 is greater than or equal to the diameter of thefirst inner conductive vias 312 a provided on the row closest to theinner periphery 302 a of the cavity 302. This distance may also begreater than or equal to the diameter of the auxiliary inner conductivevias 332 a provided on the row closest to the inner periphery 302 a ofthe cavity 302.

In these preferred embodiments of the present invention, the indirectpath is therefore maximized by making the distance X2, between theoutput side windings and the magnetic core 304, as large as possible.Overall, the electrical isolation is therefore determined by the minimumvalue of X1 and X2. This means that, for a certain minimum electricalisolation to be realized, both the distances X1 and X2 must be largerthan a predetermined value.

The spacing and positions of the conductive vias not only affects theelectrical isolation but also alters the coupling characteristics, forexample the amount of leakage inductance, between the differentwindings. This is because the leakage inductance results from imperfectmagnetic flux linking through the windings due to the magnetic flux notbeing entirely constrained within the magnetic core. Some leakageinductance is desirable because it has the effect of providing aninductance in series with the transformer windings, which combined withthe distributed capacitance that exists between adjacent transformerturns enables the transformer to act as an oscillating LC circuit, aswill be explained in more detail below in relation to FIGS. 5 and 6.

The leakage inductance can be increased by: (i) increasing the gapbetween the windings; and (ii) increasing the distance between pairs ofconnected conducting vias. Staggering the conductive vias by providingthem on more than one row allows room for an increase in the gap betweenthe windings, thereby contributing to (i), and also increases the gapbetween some of the inner and outer connected conductive vias, therebycontributing to (ii).

Increasing the gap between the first and second windings increases theamount of magnetic flux that does not couple through the windings,thereby increasing the leakage inductance. The leakage inductance canalso be increased by increasing the gap between the first and auxiliarywindings, or between the second and auxiliary windings. A combination ofany or all of these can be used. For example, the distance X1 shown inFIG. 3 can be increased to further the separation between the first andsecond windings, and between the auxiliary and second windings.

Increasing the distance between pairs of conducting vias that are, inthe complete embedded transformer, connected by conducting traces leadsto more space between the magnetic core 304 and the windings, with theresult that the magnetic flux can more easily escape. This distance isshown as X3 in FIG. 3, in relation to the second winding.

Thus, the particular configuration of conductive vias described abovebalances the requirements for isolation and leakage inductance, whileallowing the resulting embedded magnetic component transformer device tooccupy only a small footprint.

Although not shown in the figures, the leakage inductance can also beincreased by increasing the equivalent distances in relation to thefirst and/or auxiliary windings.

Staggering the conductive vias by providing them on more than one row,as is shown in FIG. 3 for the inner conductive vias of the input sidewindings, further increases the leakage inductance compared to the casewhere all of the conductive vias are provided in a single row. This isbecause such an arrangement allows more space between the conductivevias defining the outer row, making it easier for the magnetic flux toescape.

FIG. 4 shows complete first, second, and auxiliary windings formed bylinking the conductive vias together by conductive traces 313, 323, and333. The conductive traces 313, 323, and 333 shown with a solid outlineare the upper conductive traces and are provided on the first side ofthe insulating substrate 301, whereas the conductive traces 313, 323,and 333 shown with a dashed outline are the lower conductive traces andare provided on the second side of the insulating substrate 301. Thefirst winding therefore includes first outer conductive vias 311 linkedby the conductive traces 313 to the first inner conductive vias 312 a(for the outer row) and 312 b (for the inner row). In the arrangement ofFIG. 4, the turns making up the first winding alternatively pass throughfirst inner conductive vias 312 a and 312 b as they loop around thecore. Similarly, the second winding includes second outer conductivevias 321 linked by the conductive traces 323 to the second innerconductive vias 322, and the auxiliary winding includes auxiliary outerconductive vias 331 linked by the conductive traces 333 a (for the outerrow) and 333 b (for the outer row).

In FIG. 4 connections to the first, second, and auxiliary windingsrespectively may be made by traces on the top and bottom of thesubstrate (not shown) connecting to the respective vias. Furtherconductive vias can be provided through the insulating substrate to linkthese conductive regions from one side of the insulating substrate tothe other. Note that to improve the clarity of FIG. 4, the magnetic core304 is not shown and not all of the conductive vias are labelled.

In alternative preferred embodiments of the present invention, the shapeof the insulating substrate may vary. However, the shape of theinsulating material does not significantly affect the performance of thetransformer, which is determined by the position and number ofconductive vias in each of the transformer windings.

In further preferred embodiments of the present invention, the auxiliarywindings may be included within the output side windings rather than theinput side windings as described above. The isolation and leakageinductance requirements of the previous preferred embodiments may thenapply between (i) the first winding, and (ii) the second and auxiliarywindings.

The embedded magnetic component device described above with reference toFIGS. 2 to 4 has particular application to Royer circuit configurations(also known as self-oscillating push-pull circuits). The embeddedmagnetic component device allows the Royer circuit to have a high levelof electrical isolation together with short circuit protection. Such anarrangement is illustrated schematically by the circuit diagram of FIG.5.

The circuit takes a DC input between input terminals +V and GND, withthe GND terminal being held a ground potential. A resistor R1 andcapacitor C1 are connected in series across the input terminals, and anode 605 is located between them. The transformer TX1 is defined by anembedded transformer of the previously described preferred embodiments,and includes a first winding defined between nodes 610 and 614, a secondwinding defined between nodes 620 and 624, and an auxiliary windingdefined between nodes 630 and 634. Node 612 is connected partially alongthe first winding, node 622 is connected partially along the secondwinding, and node 632 is connected partially along the auxiliarywinding. In one example, the nodes connected partially along thewindings are connected to the midpoint of the respective windings. Thus,the first winding is divided into two windings 611 and 613, the secondwinding is divided into two windings 621 and 623, and the auxiliarywinding is divided into two windings 631 and 633.

Two transistors TR1 and TR2 are provided to switch in and out anenergizing voltage across the two portions of the first windings 613 and611 respectively. The transistors shown are npn-type but other types arepossible. High power switching transistors, for example, MOSFETs (metaloxide semiconductor field effect transistors) are suitable. Thecollector of transistor TR1 is connected to a first end of the firstwinding at node 610, and the collector of transistor TR2 is connected toa second end of the first winding at node 614. The emitter of transistorTR1 is connected to one terminal of inductor L2, and the other terminalof inductor L2 is connected to node 602. The emitter of transistor TR2is connected to one terminal of inductor L1, and the other terminal ofinductor L1 is connected to node 602. Node 602 is connected to node 603,which is held at ground potential. A first terminal of capacitor C2 isconnected to node 603, and the other terminal is connected to node 604which is connected directly to the high voltage input +V. Between node604 and node 612 a resistor R3 is provided.

It may be desirable to add a further inductance or capacitance to theembedded transformer by way of the circuit components in FIG. 5. Toincrease the leakage inductance of the transformer, for example, aninductance may also be provided in series with the resistor R3, or atnodes 610, 612, 614. A ferrite bead may be used as the additionalinductor, in place of, or in addition to, the resistor R3. Additionally,a capacitor may be added to the circuit connected to nodes 610, 612 or614. By adding inductance or capacitance to the input side, the LCproperties of the transformer, and the oscillating circuit formed by thetransformer and the circuitry of FIG. 5, can be fine-tuned.

Each end of the auxiliary coil is connected to one of the bases of thetransistors. Thus, node 630 is connected to the base of transistor TR1,and node 634 is connected to the base of transistor TR2. Node 632 isconnected to the first terminal of resistor R2, the second terminal ofresistor R2 being connected to node 605.

The circuit oscillates between energizing the winding 611 and energizingthe winding 613. When winding 613 is energized, the increasing magneticflux passing through the core of transformer TX1 induces a voltageacross the auxiliary windings 631 and 633. The induced voltage acrossauxiliary winding 631 is of the correct polarity to apply a voltage tothe base terminal of transistor TR1 in order to keep transistor TR1switched on. A positive feedback arrangement is thereby achieved, withTR1 being switched on and TR2 being switched off. Eventually themagnetic field within the core saturates and the rate of change ofmagnetic flux within it drops to zero. The voltage across the firstwinding 613, and therefore the current flowing through it, also drops tozero. The auxiliary windings 631 and 633 react to this change and aninduced voltage, of reverse polarity, is set up across them. This hasthe effect of switching on transistor TR2 and switching off transistorTR1, thereby energizing the winding 611. Again, positive feedback is setup such that the voltage applied to the base of transistor TR2 by theauxiliary winding 633 maintains transistor TR2 in a switched on state,while keeping transistor TR1 in a switched off state. Following this,the magnetic field within the core saturates and the circuit returns toenergizing the winding 613. This oscillatory behavior, alternatingbetween energizing the first windings 611 and 613, continuesindefinitely as long as input power is provided.

On the output side of the transformer TX1, a diode D1 has one terminalconnected to node 620 and the other connected to node 606, and is biasedin a direction towards the node 606. A diode D2 is also provided, havingone terminal connected to node 624 and the other connected to node 606,and again is biased in a direction towards the node 606. Node 622 isdirectly connected to node 608, and node 606 is directly connected tonode 607. A capacitor C3 is provided between the nodes 607 and 608. Node607 is connected to first output terminal 640, and node 608 is connectedto second output terminal 642.

The second windings 621 and 623 have voltages induced across themaccording to the rate of change of magnetic flux within the transformercore. Thus, an alternating current is set up through the combinedwindings 621 and 623. When this current circulates in a first direction,diode D1 is forward biased and current flows into node 622, throughwinding 621, and out of node 620, and a voltage is set up across theoutput terminals 640 and 642. Diode D2 is reverse biased so no currentis able to flow through winding 623. When the alternating currentcirculates in a second direction, diode D2 is forward biased and currentflows into node 622, through winding 623, and out of node 624, therebyagain applying a voltage of the same polarity across the outputterminals 640 and 642. The diodes D1 and D2 thereby rectify thealternating current, and the capacitor C3 smooths the output to providean approximately constant direct current between the output terminals640 and 642. The circuit illustrated in FIG. 5 is therefore an isolatedDC to DC converter, taking a DC input across terminals +V and GND, andgenerating a DC output across terminals 640 and 642. The voltage of theDC output relative to that of the DC input can be adjusted by varyingthe number of turns on the first 611, 613 and second 621, 623 windings.

Although in the preferred embodiment of FIG. 5 the embedded transformerdevice is included in a Royer circuit, it should be noted that itsadvantages may be realized in any power converter circuit topologycontaining an embedded transformer.

As the embedded transformer device according to various preferredembodiments of the present invention has a large leakage inductance, theembedded transformer and driving circuit, for example, the Royer circuitof FIG. 5, can activate a short circuit mode when necessary. This willbe described in more detail below and with reference to FIG. 6.

When the transformer is shorted out, meaning that a short circuit occurscorresponding to a breakdown in the isolation between input side andoutput side windings, the inductance of the first winding drops toapproximately zero. Therefore, the leakage inductance L_(leakage) andthe distributed capacitance set up between the transformer windingsC_(distributed) form an oscillating LC circuit with resonant frequency:ω₀=(L _(leakage) C _(distributed))^(−1/2).

By adjusting the leakage inductance one can tune the resonant frequencyof such a circuit. It is also possible to tune the resonant frequency byadjusting the distributed capacitance. However, this requiresrearranging the vias and adjusting the spacing between them, which maynot be possible due to space constraints on the substrate or PCB of thetransformer.

FIG. 6 shows a plot 710 of the voltage across a measurement coilincluding two turns wound upon the magnetic core 304. This voltage isplotted on the y-axis against time on the x-axis. The y-axis graduationsshow volts and x-axis graduations show nanoseconds. The high-frequencyoscillations are clearly visible.

The high-frequency oscillation mode that the transformer enters when ashort circuit occurs serves to limit the amount of power transferredbetween the windings, for example between the first winding and thesecond winding, with the result that the usual high currents thataccompany a short circuit are not present. As these high currents damagethe electrical components through which they pass, for example switchingtransistors connected to the embedded transformer, damage to theelectrical components is avoided by use of this mode. The high-frequencyoscillation mode has the advantage that it is inherent to thetransformer itself, rather than originating from any other externalcircuitry designed to switch out high currents that are present when ashort circuit occurs. It therefore ensures that the embedded transformerand associated components are always protected against short circuits,and avoids the possibility that any external circuitry may fail therebypreventing adequate short circuit protection.

Furthermore, the transformer can withstand being in a short circuitcondition continuously, for an extended period of time, simply bymaintaining the high-frequency mode of oscillation and thereby avoidingdamage to the electrical components until such a time as the shortcircuit is no longer present and the electrical components will not bedamaged. The transformer then returns to its normal operation.

Although reference is made to conductive vias throughout the presentapplication, it should be noted that any conductive connector, forexample, conductive pins, can equally well be used in place of any oneor more of the conductive vias. Furthermore, the first and secondwindings can each either be primary transformer windings being connectedto the input power supply of the transformer, or secondary transformerwindings being connected to the output of the transformer. The embeddedtransformer device can be either a step-up or step-down transformer.

Further, although, in the examples above, the magnetic core 304 andcavity 302 are illustrated as being circular or substantially circularin shape, it may have a different shape in other preferred embodimentsof the present invention. Non-limiting examples include, an oval orelongated toroidal shape, a toroidal shape having a gap, EE, EI, I, EFD,EP, UI and UR core shapes. The magnetic core 304 may be coated with aninsulating material to reduce the possibility of breakdown occurringbetween the conductive magnetic core and the conductive vias or metallictraces. The magnetic core may also have chamfered edges providing aprofile or cross section that is rounded.

In the description above, a converter has been described with 16 turnson the primary side windings, and nine turns on the secondary side as anon-limiting example. In other preferred embodiments of the presentinvention, different numbers of turns on the primary and secondary sidemay be used. Known Royer circuits, for example, may include 16 turns forthe primary side and 18 turns for the secondary side. The transformerillustrated in FIG. 4 therefore reduces the number of turns required forthe secondary side by substituting the known Royer circuit output for asynchronized rectifier circuit. In alternative preferred embodiments,the transformer in FIG. 4 may be adapted so that the primary side turnsare reduced, using a half bridge circuit on the input side and a normalRoyer output on the secondary side. This would reduce the number ofturns needed for the transformer by 6 on the primary side compared withthe known Royer circuit device. Alternatively, both of the primary andsecondary windings could have reduced turns, by using a half bridgecircuit on the primary side, and a synchronized rectifier circuit on theoutput. This would reduce the number of turns required from the knownRoyer circuit configuration by 13. In all cases, reducing the number ofturns means more flexibility in the design layout and higher potentialisolation between the components. However, reducing secondary turnsrequires only one additional transistor (e.g. in a FET dual package) tobe added to the circuit. Reducing the primary side windings requires ahalf bridge circuit to be provided meaning more components on the inputside compared with the known Royer design.

Various modifications to the preferred embodiments described above arepossible and will occur to those skilled in the art without departingfrom the scope of the invention which is defined by the followingclaims.

It should be understood that the foregoing description is onlyillustrative of the present invention. Various alternatives andmodifications can be devised by those skilled in the art withoutdeparting from the present invention. Accordingly, the present inventionis intended to embrace all such alternatives, modifications, andvariances that fall within the scope of the appended claims.

The invention claimed is:
 1. An embedded transformer device, comprising:an insulating substrate including a first side and a second sideopposite the first side, and including a cavity therein, the cavityincluding an inner and an outer periphery; a magnetic core housed in thecavity including a first section and a second section; a first windingextending through the insulating substrate and around the first sectionof the magnetic core; and a second winding extending through theinsulating substrate and around the second section of the magnetic core;wherein the first winding and the second winding are located in separateregions from each other in the insulating substrate such that a firstboundary around the first winding does not overlap a second boundaryaround the second winding; each of the first and second windingsinclude: upper conductive traces located on the first side of theinsulating substrate; lower conductive traces located on the second sideof the insulating substrate; inner conductive connectors extendingthrough the insulating substrate adjacent to an inner periphery of themagnetic core, the inner conductive connectors respectively definingelectrical connections between respective upper conductive traces andrespective lower conductive traces; and outer conductive connectorsextending through the insulating substrate adjacent to an outerperiphery of the magnetic core, the outer conductive connectorsrespectively defining electrical connections between respective upperconductive traces and respective lower conductive traces; the innerconductive connectors of the first winding are arranged in a pluralityof curved rows, each of the plurality of curved rows being positioned ata constant or substantially constant distance from an inner periphery ofthe cavity; the inner conductive connectors of the second winding arearranged in a first curved row positioned at a constant or substantiallyconstant distance from the inner periphery of the cavity that is largeenough to allow a second curved row of inner conductive connectors to beaccommodated between the first curved row and the inner periphery of thecavity; and the outer conductive connectors of the second winding arearranged in a first curved row positioned at a constant or substantiallyconstant distance from the outer periphery of the cavity that is largeenough to allow a second curved row of outer conductive connectors to beaccommodated between the first curved row and the outer periphery of thecavity.
 2. The embedded transformer device of claim 1, wherein: theinner conductive connectors of the first winding on a curved row closestto the inner periphery of the cavity are arranged on a first circular orsubstantially circular arc having a first radius; the inner conductiveconnectors of the second winding on the first curved row are arranged ona second circular or substantially circular arc, concentric to the firstcircular or substantially circular arc, having a second radius; and thefirst radius is greater than the second radius.
 3. The embeddedtransformer device of claim 1, wherein the first winding is spaced apartfrom the second winding so that electrical isolation is provided betweenthe first winding and the second winding.
 4. The embedded transformerdevice of claim 1, wherein the first winding does not overlap with thesecond winding in a thickness direction of the insulating substrate. 5.The embedded transformer device of claim 1, further comprising: a firstisolation barrier located on the first side of the insulating substrate,covering at least a portion of the first side between the first windingand the second winding where the first winding and second winding areclosest, and defining a solid bonded joint with the first side of theinsulating substrate; and a second isolation barrier located on thesecond side of the insulating substrate covering at least a portion ofthe second side between the first winding and the second winding wherethe first winding and second winding are closest, and defining a solidbonded joint with the second side of the insulating substrate.
 6. Theembedded transformer device of claim 1, further comprising: an auxiliarywinding, extending through the insulating substrate and around themagnetic core, the auxiliary winding including: upper conductive traceslocated on the first side of the insulating substrate; lower conductivetraces located on the second side of the insulating substrate; innerconductive connectors extending through the insulating substrateadjacent to the inner periphery of the magnetic core, the innerconductive connectors respectively defining electrical connectionsbetween respective upper conductive traces and respective lowerconductive traces; and outer conductive connectors extending through theinsulating substrate adjacent to the outer periphery of the magneticcore, the outer conductive connectors respectively defining electricalconnections between respective upper conductive traces and respectivelower conductive traces; wherein the inner conductive connectors of theauxiliary winding are arranged in a plurality of curved rows, each ofthe plurality of curved rows being positioned at a constant orsubstantially constant distance from the inner periphery of the cavity.7. The embedded transformer device of claim 6, wherein the auxiliarywinding is spaced apart from the second winding so that electricalisolation is provided between the auxiliary winding and the secondwinding.
 8. The embedded transformer device of claim 1, whereinelectrical isolation is provided by a minimum of: a minimum distance ofseparation between the first winding and the second winding; and aminimum distance of separation between the second winding and themagnetic core.
 9. The embedded transformer device of claim 1, whereinthe constant or substantially constant distance being large enough toallow a second curved row of outer conductive connectors to beaccommodated increases a leakage inductance of the transformer device.10. The embedded transformer device of claim 1, wherein a leakageinductance of the transformer device and a distributed capacitance ofthe first and second windings define a high-frequency oscillating LCcircuit, operable to limit power transfer between the first and secondwindings when a short circuit occurs.
 11. A power converter comprisingthe embedded transformer device of claim
 1. 12. The power converter ofclaim 11, further comprising circuitry to energize the first and secondwindings, wherein the circuitry is a Royer circuit.
 13. An embeddedtransformer device, comprising: an insulating substrate including afirst side and a second side opposite the first side, and including acavity therein, the cavity including an inner and an outer periphery; amagnetic core housed in the cavity including a first section and asecond section; a first winding, extending through the insulatingsubstrate and around the first section of the magnetic core; a secondwinding, extending through the insulating substrate and around thesecond section of the magnetic core; wherein the first winding and thesecond winding are located in separate regions from each other in theinsulating substrate such that a first boundary around the first windingdoes not overlap a second boundary around the second winding; each ofthe first and second windings includes: upper conductive traces locatedon the first side of the insulating substrate; lower conductive traceslocated on the second side of the insulating substrate; inner conductiveconnectors extending through the insulating substrate adjacent to aninner periphery of the magnetic core, the inner conductive connectorsrespectively defining electrical connections between respective upperconductive traces and respective lower conductive traces; and outerconductive connectors extending through the insulating substrateadjacent to an outer periphery of the magnetic core, the outerconductive connectors respectively defining electrical connectionsbetween respective upper conductive traces and respective lowerconductive traces; the inner conductive connectors of the first windingare arranged in two or more first curved rows, each of the two or morefirst curved rows being positioned at a constant or substantiallyconstant distance from an inner periphery of the cavity; the innerconductive connectors of the second winding are arranged in one or moresecond curved rows, each of the one or more second curved rows beingpositioned at a constant or substantially constant distance from theinner periphery of the cavity; and a minimum distance between the innerconductive connectors of the second winding and the magnetic core isgreater than a minimum distance between the inner conductive connectorsof the first winding and the magnetic core.
 14. A method ofmanufacturing an embedded transformer device, comprising: a) preparingan insulating substrate including a first side and a second sideopposite the first side, and including a cavity therein, the cavityincluding an inner and an outer periphery; b) inserting a magnetic coreinto the cavity; c) forming a first winding, extending through theinsulating substrate and around a first section of the magnetic core; d)forming a second winding, extending through the insulating substrate andaround a second section of the magnetic core; wherein the first windingand the second winding are located in separate regions from each otherin the insulating substrate such that a first boundary around the firstwinding does not overlap a second boundary around the second winding;each of the first and second windings includes: upper conductive traceslocated on the first side of the insulating substrate; lower conductivetraces located on the second side of the insulating substrate; innerconductive connectors extending through the insulating substrateadjacent to an inner periphery of the magnetic core, the innerconductive connectors respectively forming electrical connectionsbetween respective upper conductive traces and respective lowerconductive traces; and outer conductive connectors extending through theinsulating substrate adjacent to the outer periphery of the magneticcore, the outer conductive connectors respectively forming electricalconnections between respective upper conductive traces and respectivelower conductive traces; e) arranging the inner conductive connectors ofthe first winding in a plurality of curved rows, each of the pluralityof curved rows being positioned at a constant or substantially constantdistance from an inner periphery of the cavity; f) arranging the innerconductive connectors of the second winding in a first curved rowpositioned at a constant or substantially constant distance from theinner periphery of the cavity that is large enough to allow a secondcurved row of inner conductive connectors to be accommodated between thefirst curved row and the inner periphery of the cavity; and g) arrangingthe outer conductive connectors of the second winding in a first curvedrow positioned at a constant or substantially constant distance from theouter periphery of the cavity that is large enough to allow a secondcurved row of outer conductive connectors to be accommodated between thefirst curved row and the outer periphery of the cavity.
 15. The methodof claim 14, further comprising: arranging the inner conductiveconnectors of the first winding on a curved row closest to the innerperiphery of the cavity on a first circular or substantially circulararc having a first radius; arranging the inner conductive connectors ofthe second winding on the first curved row on a second circular orsubstantially circular arc, concentric to the first circular orsubstantially circular arc, having a second radius; wherein the firstradius is greater than the second radius.
 16. The method of claim 14,further comprising spacing the first winding apart from the secondwinding so that electrical isolation is provided between the firstwinding and the second winding.
 17. The method of claim 14, wherein thefirst winding does not overlap with the second winding in a thicknessdirection of the insulating substrate.
 18. The method of claim 14,further comprising: providing a first isolation barrier on the firstside of the insulating substrate, covering at least a portion of thefirst side between the first winding and the second winding where thefirst winding and second winding are closest, and defining a solidbonded joint with the first side of the insulating substrate; andproviding a second isolation barrier on the second side of theinsulating substrate covering at least a portion of the second sidebetween the first winding and the second winding where the first windingand second winding are closest, and defining a solid bonded joint withthe second side of the insulating substrate.
 19. The method of claim 14,further comprising: forming an auxiliary winding, extending through theinsulating substrate and around the magnetic core, the auxiliary windingincluding: upper conductive traces located on the first side of theinsulating substrate; lower conductive traces located on the second sideof the insulating substrate; inner conductive connectors extendingthrough the insulating substrate adjacent to the inner periphery of themagnetic core, the inner conductive connectors respectively definingelectrical connections between respective upper conductive traces andrespective lower conductive traces; and outer conductive connectorsextending through the insulating substrate adjacent to the outerperiphery of the magnetic core, the outer conductive connectorsrespectively defining electrical connections between respective upperconductive traces and respective lower conductive traces; and arrangingthe inner conductive connectors of the auxiliary winding in a pluralityof curved rows, each of the plurality of curved rows being positioned ata constant or substantially constant distance from the inner peripheryof the cavity.
 20. The method of claim 19, further comprising spacingthe auxiliary winding apart from the second winding so that electricalisolation is provided between the auxiliary winding and the secondwinding.